The ability to control transport of chemical species across cellular membranes is important from a therapeutic standpoint inasmuch as a number of disease conditions, including glaucoma and certain kidney and stomach disorders, are directly related to such transport. In addition, a better understanding of the mechanisms for such transport can be expected to yield improved therapeutic and diagnostic tools.
It is thought that transport of ions, including Na.sup.+, across membranes is controlled in part by membrane channel proteins which exist in certain membranes and which act to transport or "channel" ions across such membranes. Only about six or so protein channels have actually been isolated. Epithelial Na.sup.+ channel proteins have been discussed by Palmer in J. Membrane Biol., Vol. 96, pp. 97-106 (1987). Agents which selectively block ion transport have been described, as for example amiloride (3,5-diamino-N-(aminoiminomethyl)-6-chloropyrazinecarboxamide). Amiloride is widely thought to interact with a Na.sup.+ /H.sup.+ exchanger at high concentrations and a Na.sup.+ channel protein at much lower concentrations. By utilizing the channel protein binding compound amiloride in affinity gels, it has been shown in investigations relating to the present invention to be possible to isolate and purify the Na.sup.+ channel protein. Both the channel protein and the binding compounds and associated affinity gels are useful in therapeutic control of membrane transport or in developing assays related to membrane control.
The full disclosure and claims of applicant's copending U.S. patent application, Ser. No. 948,262, is incorporated herein by reference.